Yogodin et al., Dold. Akad. Nauk SSR, 249, No. 4, (1979), pp. 915-919, showed that the direct fluorinations of WO.sub.3, UF.sub.4 and UO.sub.2 F.sub.2 were greatly enhanced by additions of NiF.sub.2 powder to the solid reactants. Among the findings of Yogodin et al. is that both catalyzed and uncatalyzed reactions fit the "Diminishing Sphere" model: EQU 1-(1-F).sup.1/3 =R't (1)
wherein F is the fraction of the completed reaction, t is time, and R' is an apparent rate constant dependent on temperature and surface area. Rates increased rapidly with catalyst addition and reached a maximum at between weight ratios, M.sub.o, of 0.25 and 1.0 of catalyst to reactant, activation energies for catalyzed and uncatalyzed reactions did not change, and the catalyst decreased the F.sub.2 pressure dependence from one to 0.5 to 0.7.
Similar findings were reported by Maeda and Yagi, Inorg. Nucl. Chem. Lett., 14, no. 10, (1978), pp. 341-345, studying the direct fluorination of UO.sub.2 mixed with simulated fission products, but the identity of the catalyst(s) was not determined. The catalyst was disclosed to contain silver. AgO.sub.2 was added as one of may constituents of the simulated fission products FP-II in Maeda and Yagi. Many other metal oxides were also added, and the mix was thoroughly fluorinated before use. It is possible that such fluorination converted the AgO.sub.2 and other metal oxides into their respective fluorides--so AgF.sub.2 would very probably be one of the constituents of the mix. Since many fluorides and possibly oxides were also present in the mix, which one or ones of such fluorides and/or oxides actually caused the catalysis cannot be determined from Maeda and Yagi.